1. Field of the Invention
This invention relates to automatic power transmissions providing a plurality of gear reduction ratios, such as automatic mechanical transmissions, and to control systems therefor. In particular, the present invention relates to control systems for vehicles with throttle controlled engines and automatic transmissions wherein gear selection and shift decisions are made and executed based upon measured and/or calculated parameters such as vehicle or output shaft speed, input shaft or engine speed, throttle position, and the like. More particularly, the present invention relates to an automatic transmission control having a mode of operation, selectable by the operator, for high resistance operation wherein upshifts to a higher drive gear will only occur if, at a selected throttle position such as the current throttle position, the expected output power of the engine, after the shift, is at least equal to the engine output power prior to the shift.
2. Description of the Prior Art
The use of automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches is well known in the prior art as are control systems therefor. Electronic control systems for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), acutation of the braking mechanism, currently engaged gear ratio, and the like are known in the prior art. Examples of such automatic transmission control systems for vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,073,203; 4,253,348; 4,038,889; 4,226,295; 3,776,048; 4,208,929; 4,039,061; 3,974,720 and 3,942,393, all hereby incorporated by reference.
While the above referenced automatic transmission control systems, and similar systems, are effective to control an automatic transmission by selecting a desired gear ratio which will tend to optimize the fuel economy and/or performance of the vehicle in view of the sensed parameters and then to commanding a shift into the selected gear ratio, such control systems were not totally acceptable as the predetermined programs utilized to generate a shift pattern, or patterns (also commonly referred to as a shift point profile) were, at best, a compromise of fuel efficiency operation and desirable vehicle performance operation, did not provide an operator selectable automatic mode for off-road high rolling resistance vehicle operation and/or did not provide shift patterns for the off-road mode of operation which assured that the engine power output, for a given throttle position, after an upshift was at least equal to the engine power output prior to the upshift.